Resonance control apparatus for a piezoelectrical device based on phase sensitive detection

ABSTRACT

A resonance control apparatus  100  includes a VCO  10  which generates a reference signal having a predetermined frequency, a divider  20  which divides the predetermined frequency of the reference signal, a phase reference forming section  50  which delays a phase of the divided signal for a predetermined interval, a voltage comparator  40  which compares a voltage of the output signal from a piezoelectric sensor  2  for detecting the driving state of a piezoelectric load  3  in synchronization with the driving of the piezoelectric load  3  with a predetermined voltage, a phase comparator 60 which compares the phase of the output signal from the voltage comparator  40  with the phase of the output signal from the phase reference forming section  50,  and a duty control section  30  for controlling a duty ratio of the drive signal supplied to the piezoelectric load 3 based on the reference signal.

TECHNICAL FIELD

The present invention relates to a resonance control apparatus and amethod of controlling the same.

BACKGROUND ART

In a resonance control apparatus such as a driving device using apiezoelectric effect of a piezoelectric element (as a ultrasonic motor,including ones disclosed in Japanese Laid-Open Patent Application No.HEI. 3-243183 and Japanese Laid-Open Patent Application No. HEI.3-289375, for example), and a display device using a piezoelectriceffect, a resonant point of a resonant frequency at which the driveefficiency is maximized may undergo a change due to the piezoelectriccharacteristic, temperature characteristic, structural characteristic ofthe peripheral mechanics or the like.

Therefore, in a conventional resonance control apparatus, the drivingstate of the load is detected as a potential (voltage value) using apiezoelectric sensor, the detected voltage value of the output signalfrom the piezoelectric sensor is integral-operated using a CPU(processor), a driving frequency of the load is heightened and/orlowered until the operated result (integrated value of the potential)leads to the substantially maximum value, and the frequency when theoperated result becomes maximum is utilized as a resonant frequency.

Here, the structure of a conventional resonance control apparatus willbe described with reference to FIG. 11. FIG. 11 is a block diagramschematically illustrating a main portion of the conventional resonancecontrol apparatus 200. As shown in FIG. 11, the conventional resonancecontrol apparatus 200 includes a central processing unit (CPU) 1, anamplifier section 4, a gain control amplifier section 5, a voltagecontrolled oscillator (VCO) 10, an analog-digital converter (ADC) 6, andtwo digital-analog converters (DAC) 7, 8. Further, the conventionalresonance control apparatus 200 is connected to a piezoelectric sensor 2and a piezoelectric element (piezoelectric load) 3 via the amplifiersection 4 and the gain control amplifier section 5, respectively.

As described above, the voltage value (potential data) of the drivingstate of the piezoelectric load 3, which is outputted from thepiezoelectric sensor 2, is amplified by the amplifier section 4, andconverted into a digital data by the ADC 6 to input into the CPU 1. TheCPU 1 carries out an integral operation of the voltage value inputtedfrom the ADC 6, and heightens the frequency of a drive signal for thepiezoelectric load 3 until the voltage value reaches a resonantfrequency region of the piezoelectric sensor 2 (see FIG. 3). During therising of the frequency of the drive signal, the CPU 1 outputsinstantaneous voltage value data to the VCO 10 via the DAC 7, and thenthe VCO 10 generates the drive signal for the piezoelectric load 3having a predetermined frequency in response to the inputted voltagevalue data to output the drive signal to the gain control amplifiersection 5.

The gain control amplifier section 5 adjusts the gain of the drivesignal generated in the VCO 10 based on a delay control signal that isinputted from the CPU 1 via the DAC 8, delays the phase of the drivesignal so that the phase of the drive signal synchronizes with the phaseof detected signal outputted from the piezoelectric sensor 2 (thisprocess corresponds to delay process), and outputs the drive signalwhose phase was delayed by the gain control amplifier section 5 to thepiezoelectric load 3.

Subsequently, when the CPU 1 judges that the integral-operated value ofthe voltage value at a given frequency substantially reaches a maximumvalue by heightening and/or lowering the frequency of the drive signal,the CPU 1 determines that the given frequency is a resonant point of thepiezoelectric load 3, i.e., the frequency of the drive signal reachesthe resonant frequency of the piezoelectric load 3 (this processcorresponds to frequency determination process), and outputs the voltagevalue at the resonant point to the VCO 10 via the DAC 7. The VCO 10outputs the drive signal having the frequency corresponding to thevoltage value (i.e., resonant frequency) to the gain control amplifiersection 5. After gain control process and phase delay process arecarried out in the gain control amplifier section 5, the piezoelectricload 3 is driven by the resulting drive signal. In this way, theconventional resonance control apparatus 200 controls the driving of thepiezoelectric load 3 with the drive signal having the resonant frequencyafter the resonant frequency is obtained.

However, in the conventional resonance control apparatus 200, in thecase where a rapid drive control such as posture control is implemented,it takes quite a long time to obtain the resonant frequency of thepiezoelectric load 3 by gradually heightening the frequency of the drivesignal as described above because the CPU 1 carries out theabove-mentioned operated process. Therefore, there is a problem thatunstable state of control, namely, the state in which the CPU 1 iscarrying out the operated process is frequently taken place.

Further, since the conventional resonance control apparatus 200 includesanalog peripheral circuits such as the ADC 6, the DACs 7, 8, and thelike, there is a problem that it is difficult to integrate thesecircuits into an IC chip for digital operation.

Moreover, since the conventional resonance control apparatus 200includes the CPU 1 for carrying out the operated process, the systemincluding the CPU 1 becomes a big deal. Therefore, there is a problemthat it is difficult to make a circuit dimension (circuitry) small (todownsize the circuit dimension).

DISCLOSURE OF INVENTION

In view of the above-mentioned problems of the prior art, it istherefore an object of the present invention to provide a resonancecontrol apparatus and a method of controlling a resonant device whichcan control the rest or movement of an object in the posture controlquickly because it takes quite a short time to obtain a resonantfrequency of the resonant device, and can downsize the circuitry of theresonance control apparatus because it is easy to integrate the controlsections thereof into an IC chip.

In order to achieve the above object, in one aspect of the presentinvention, the present invention is directed to a resonance controlapparatus for driving a resonant device having a resonancecharacteristic. The resonant device functions as a resonant sensor. Theresonance control apparatus comprises:

a reference signal generating section for generating a reference signalhaving a predetermined frequency in response to a voltage signal that isinputted into the reference signal generating section;

a divider which divides the predetermined frequency of the referencesignal generated by the reference signal generating section to output asignal having a given frequency;

a phase reference forming section which delays a phase of the signaloutputted from the divider for a predetermined interval;

a voltage comparator for comparing a voltage of the output signal fromthe resonant sensor with a predetermined voltage, the resonant sensordetecting the driving state of the resonant device in synchronizationwith the driving of the resonant device;

a phase comparator for comparing the phase of the signal outputted fromthe voltage comparator with the phase of the signal outputted from thephase reference forming section; and

a duty control section for controlling a duty ratio of the drive signalprovided for the resonant device based on the reference signal outputtedfrom the reference signal generating section.

In the resonance control apparatus of the present invention, theresonant device is driven by self-controlling the frequency of the drivesignal for the resonant device using the output signal from the resonantsensor as a feedback value. Therefore, according to the resonancecontrol apparatus of the present invention, it is possible to shorten(reduce) the time required to obtain the resonant frequency of theresonant device, thereby being capable of controlling the rest ormovement of an object in the posture control quickly (i.e., capable ofcontrolling a duty ratio of the drive signal). Further, it is possibleto integrate the control sections of the resonance control apparatusinto an IC chip, thereby being capable of downsizing the circuitry ofthe resonance control apparatus.

In this case, it is preferred that the resonance control apparatusfurther comprises a low-pass filter which cuts out a high frequencycomponent of the output signal from the phase comparator wherein theoutput signal from the low-pass filter constitutes the voltage signalinputted into the reference signal generating section.

Further, it is preferred that the phase reference forming section isconstructed so as to be capable of selecting either a rising edge ortrailing edge of the signal delayed in the phase reference formingsection when the phase comparator compares the phases, based on the dutyratio of the drive signal controlled by the duty control section.

Moreover, it is preferred that the duty control section drives theresonant device with the duty ratio in the range of either 10%-50% or50%-90%.

Further, it is preferred that the output signal from the resonant devicecorresponds to a resonant frequency of the resonant device, and thefrequency of the drive signal outputted from the duty control section iscontrolled so as to be equal to the resonant frequency.

In this case, it is preferred that the resonance control apparatuscarries out the PWM control for the resonant device based on the dutyratio of the drive signal controlled by the duty control section.

Further, in this case, it is preferred that the PWM control is carriedout so as to maintain the resonant frequency of the resonant device.

Further, it is preferred that the resonance control apparatus furthercomprises a first phase correction section arranged between the voltagecomparator and the phase comparator, the first phase correction sectioncorrecting the phase of the signal outputted from the voltage comparatorto output the phase-corrected signal to the phase comparator.

In this case, it is also preferred that the resonance control apparatusfurther comprises a second phase correction section for correcting thephase of the output signal from the duty control section in response tothe phase of the resonant frequency of the resonant device.

In another embodiment of the present invention, it is preferred that theresonance control apparatus further comprises a second duty controlsection having a function same as the duty control section, the secondduty control section being arranged in parallel with the duty controlsection;

wherein the two duty control sections are respectively provided fornormal drive and reverse drive of the resonant devices, and can controlthe duty ratios of the drive signals for normal drive and reverse driveeither independently or jointly.

Alternatively, it is preferred that the resonance control apparatusfurther comprises at least one duty control section having a functionsame as the duty control section arranged in parallel with the dutycontrol section;

wherein at least two duty control sections among the duty controlsection and the at least one duty control section are provided fornormal drive of the resonant devices, and can control the duty ratio ofthe drive signals for normal drive either independently or jointly.

The present invention is directed to a resonance control apparatus fordriving a resonant device having a resonance characteristic. Theresonant device functions as a resonant sensor. The resonance controlapparatus compares the phase of a drive signal for the resonant devicewith the phase of an output signal from the resonant sensor, which isutilized as a feedback value for the resonant device, and outputs thedrive signal to the resonant device in response to the differencebetween the phases.

Further, in another aspect of the present invention, the presentinvention is directed to a method of controlling a resonant devicehaving a resonance characteristic. The resonant device functions as aresonant sensor. The method comprises the steps of:

generating a reference signal having a predetermined frequency inresponse to a voltage signal to be inputted, the reference signal beinga drive signal for the resonant device;

dividing the predetermined frequency of the reference signal to output asignal having a given frequency;

delaying a phase of the output signal for a predetermined interval;

comparing a voltage of the output signal from a resonant sensor with apredetermined voltage to output a voltage comparison signal, theresonant sensor detecting the driving state of the resonant device insynchronization with the driving of the resonant device; and

comparing the phase of the voltage comparison signal with the phase ofthe delayed signal to output a phase comparison signal, the phasecomparison signal corresponding to the voltage signal to be inputted.

In the present invention, it is preferred that the method furthercomprises the steps of:

controlling a duty ratio of the drive signal supplied to the resonantdevice; and

carrying out the PWM control for the resonant device using the dutyratio of the drive signal.

In this case, it is preferred that the duty ratio controlling stepincludes respectively controlling duty ratios of two types of drivesignals supplied to two resonant devices, which are provided for normaldrive and reverse drive of the two resonant devices, based on thereference signal, and the PWM control carrying out step includescarrying out the PWM control for the two resonant devices using the dutyratios of the drive signals.

Alternatively, it is preferred that the duty ratio controlling stepincludes respectively controlling duty ratios of at least two drivesignals for normal drive supplied to at least two resonant devices basedon the reference signal either independently or jointly, and the PWMcontrol carrying out step includes carrying out the PWM control for theat least two resonant devices using the duty ratios of the at least twodrive signals.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing and other objects, features and advantages of theinvention will become more readily apparent from the following detaileddescription of preferred embodiments of the invention which proceedswith reference to the accompanying drawings.

FIG. 1 is a schematic block diagram illustrating a main portion (circuitdiagram) of a resonance control apparatus according to the presentinvention.

FIG. 2 shows timing charts illustrating output waveforms of componentsin the resonance control apparatus shown in FIG. 1.

FIG. 3 is a graph illustrating a resonant frequency characteristic of apiezoelectric load.

FIG. 4 is a graph schematically illustrating the relationship between aduty ratio and drive vector ratio of the drive signal.

FIG. 5 is a diagram illustrating the relationship between the duty ratiocontrolled by the duty control section and the phase comparing positiondetermined by the phase reference forming section.

FIG. 6 is a diagram schematically illustrating an example of a circuitryof the driver shown in FIG. 1.

FIG. 7 is a diagram schematically illustrating waveforms of signals inthe case where a drive analog control signal to be supplied to drive thepiezoelectric load is one whose output is raised to a predeterminedoutput level at a given rate.

FIGS. 8(A) and 8(B) are diagrams illustrating the structures in whichtwo vibrating elements each including a piezoelectric element that iscontrolled by the resonance control apparatus according to the presentinvention rotate a rotor.

FIG. 9 is a diagram illustrating the partial structure of the resonancecontrol apparatus according to the present invention in the case ofusing the two vibrating elements shown in FIG. 8(A).

FIG. 10 is a diagram illustrating waveforms of the signals for normaldrive and reverse drive respectively controlled by normal-driving andreverse-driving duty control sections in response to a reference signal.

FIG. 11 is a block diagram schematically illustrating a main portion ofa conventional resonance control apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

A detailed description of the preferred embodiments of a resonancecontrol apparatus and a method of controlling a resonant deviceaccording to the present invention will now be made with reference toFIGS. 1-10. Now, it should be noted that the embodiments (disclosure)are to be considered as an exemplification, and therefore this featureshould not be intended to limit the present invention to the specificembodiments illustrated.

First, a description will be given for the structure of the resonancecontrol apparatus 100 of the present invention. FIG. 1 is a schematicblock diagram illustrating a-main portion (circuit diagram) of theresonance control apparatus 100 according to the present invention. Asshown in FIG. 1, the resonance control apparatus 100 includes a voltagecontrolled oscillator (VCO) 10, a divider 20, a duty control section 30,a voltage comparator 40, a phase reference forming section 50, a firstphase correction section (phase correction A) 51, a second phasecorrection section (phase correction B) 52, a phase comparator 60, alow-pass filter (LPF) 70, a driver 80, and a reference voltage settingsection 90 for setting a voltage value that is a reference voltage forthe voltage comparator 40. In this regard, a piezoelectric load(resonant device) 3 whose drive is controlled by means of the resonancecontrol apparatus 100 is connected to the driver 80, and a piezoelectricsensor (resonant sensor) 2 for detecting the driving state of thepiezoelectric load 3 in synchronization with the driving of thepiezoelectric load 3 is connected to one input terminal of the voltagecomparator 40. A detailed description of each component is given below.In this case, as shown in FIG. 1, a central processing unit (CPU) 1controls the divider 20, the duty control section 30, the phasereference forming section 50, the first phase correction section 51, andthe second phase correction section 52.

The VCO 10 generates a reference signal having a predetermined frequencybased on the output signal (voltage signal) from the phase comparator 60described later whose high frequency component is cut out by the LPF 70,and outputs the reference signal. The output signal from the VCO 10 isinputted to the divider 20, the duty control section 30, the phasereference forming section 50, and the first phase correction section 51.

The divider 20 divides the frequency of the reference signal that is theoutput signal from the VCO 10 by a predetermined value. The outputsignal from the divider 20 whose frequency is divided is inputted to thephase reference forming section 50, and the second phase correctionsection 52. In this regard, the dividing ratio of the divider 20 iscontrolled by the CPU 1.

The duty control section 30 controls a duty ratio of a drive signal forthe piezoelectric load 3 by control of the CPU 1. The output signal fromthe duty control section 30 is inputted to the second phase correctionsection 52. The second phase correction section 52 controls the settingof the duty ratio of the output signal from the divider 20 based on acontrol signal inputted from the duty control section 30 to output thesignal (this is the drive signal) to the driver 80. Then, the driver 80inputs the drive signal to the piezoelectric load 3 to control thedriving of the piezoelectric load 3. In this regard, the relationshipbetween the duty ratio and drive vector ratio of the piezoelectric load(piezoelectric element) 3 will be described later (see FIG. 4).

The piezoelectric sensor 2 detects the driving state of thepiezoelectric load 3 in synchronization with the driving of thepiezoelectric load 3. The detected signal (voltage signal) that is theoutput signal from the piezoelectric sensor 2 is inputted to one inputterminal of the voltage comparator 40. Further, a voltage signal that isthe reference for voltage comparison in the voltage comparator 40 is setby the reference voltage setting section 90 to input the referencevoltage to the other input terminal of the voltage comparator 40. Inthis case, in the present embodiment, the reference voltage settingsection 90 is consisted of two resistors or variable resistors and aconstant voltage source. The voltage value of the reference voltagesignal may be set manually in the case where the reference voltagesetting section 90 includes one or two variable resistor(s). However,the present invention is not limited to this structure. For example, thevoltage value may be controllable by the CPU 1. The voltage value of thereference voltage signal (this is a predetermined voltage value, i.e.,threshold for the voltage comparison) is previously set based on theresonant frequency characteristic of the piezoelectric load 3 to beutilized. The detailed description thereof will be described later.

The voltage comparator 40 compares the output signal from thepiezoelectric sensor 2 (i.e., detected signal) with the referencevoltage signal. Then, in the case where the voltage value of the outputsignal from the piezoelectric sensor 2 is larger than the voltage valueof the reference voltage signal, the voltage comparator 40 outputs ahigh-level signal to the first phase correction section 51. On the otherhand, in the case where the voltage value of the output signal issmaller than the voltage value of the reference voltage signal, thevoltage comparator 40 outputs a low-level signal to the first phasecorrection section 51. Namely, the voltage comparator 40 digitizes theoutput signal from the piezoelectric sensor 2 to output the digitizedsignal (i.e., high-level or low-level signal) to the first phasecorrection section 51.

The phase reference forming section 50 delays the phase of the outputsignal from the divider 20 for a predetermined interval (time), andselects either a rising edge or a trailing edge of the delayed signalbased on the duty ratio of the drive signal controlled by the CPU 1 andthe duty control section 30. The delayed signal outputted from the phasereference forming section 50 is inputted to one input terminal of thephase comparator 60. In this regard, the operation of the phasereference forming section 50 will be described later.

The first phase correction section 51 delays the phase of the voltagecomparison signal inputted from the voltage comparator 40 by control ofthe CPU 1. The delayed signal outputted from the first phase correctionsection 51 is inputted to the other input terminal of the phasecomparator 60. In this way, since the resonance control apparatus 100can delay the phase of each of the signals inputted to the phasecomparator 60 via the two input terminals thereof by means of the phasereference forming section 50 and the first phase correction section 51,the signal inputted from the phase reference forming section 50 can bealso adjusted so that the inputted signal is apparently led.

The phase comparator 60 compares the phase of the signal inputted fromthe first phase correction section 51 with the phase of the signalinputted from the phase reference forming section 50. Then, as shown inFIG. 2 described later, the phase comparator 60 outputs a high-levelsignal to the LPF 70 in the case where the phase point of the outputsignal from the first phase correction section 51 (i.e., the point ofthe rising edge on the time axis) is earlier than the phase point of theoutput signal from the phase reference forming section 50 (i.e., properphase point). On the other hand, the phase comparator 60 outputs alow-level signal to the LPF 70 in the case where the phase point of thefirst phase correction section 51 is later than the phase point of thephase reference forming section 50. In this regard, in the case whereboth the two signals inputted to the phase comparator 60 are in highlevel (i.e., Hi-Z), the phase comparator 60 outputs the signalcorresponding to zero level. Namely, the phase comparator 60 outputs aternary (three-valued) signal to the LPF 70 in response to the twosignals inputted from the phase reference forming section 50 and thefirst phase correction section 51.

The LPF 70 cuts out a high frequency component of the phase comparisonsignal (three-valued signal) inputted from the phase comparator 60 tooutput the voltage signal whose high frequency component is cut out tothe VCO 10. In this way, the resonance control apparatus 100 controlsthe frequency of the drive signal (i.e., the resonant frequency) byfeeding back the driving state of the piezoelectric load 3 that isdetected by the piezoelectric sensor 2 to the VCO 10 that is thereference signal generating section.

Here, by the thought that the output signal from the voltage comparator40 is a reference signal outputted from a base oscillator (basefrequency generating section), the VCO (reference signal generatingsection) 10, the divider 20, the voltage comparator 40, the phasecomparator 60, and the LPF 70 constitute a sort of PLL circuit (In ageneral PLL circuit, the frequency of a reference signal generated byand outputted from a base oscillator (base frequency generating section)is not changeable (i.e., does not undergo a change), but in this circuit(the sort of PLL circuit), the frequency of a reference signal ischangeable because a detected signal outputted from the piezoelectricsensor 2 is utilized as the reference signal. In this point, thiscircuit differs from the general PLL circuit.). In this way, since theresonance control apparatus 100 is constructed to include the sort ofPLL circuit (the circuit having a function similar to that of thegeneral PLL circuit) therein, the resonance control apparatus 100 cangenerate a reference signal having the phase-locked frequency N times asthe frequency of the drive signal for the piezoelectric load 3 (i.e.,the drive frequency) (where “N” is a value arbitrarily set by the CPU1).

Next, a description will be given for the operation of the resonancecontrol apparatus 100 of the present invention with reference to timingcharts shown in FIG. 2. FIG. 2 shows timing charts illustrating outputwaveforms of the components in the resonance control apparatus 100 shownin FIG. 1. In these timing charts, FIG. 2(A) shows a waveform of theoutput signal from the VCO 10 which is a reference signal, FIG. 2(B)shows a waveform of the output signal from the divider 20 which isobtained by dividing the reference signal by means of the divider 20,FIG. 2(C) shows a waveform of the output signal from the piezoelectricsensor 2, FIG. 2(D) shows a waveform of the output signal from thevoltage comparator 40, FIG. 2(E) shows a waveform of the output signalfrom the phase reference forming section 50, FIG. 2(F) shows a waveformof the output signal from the phase comparator 60, and FIG. 2(G) shows awaveform of the output signal from the LPF 70. As shown in FIGS. 2(B)and 2(D), the rising point (rising timing) of the output signal from thedivider 20 is delayed to a proper phase point by means of the phasereference forming section 50.

As shown in FIG. 2(C), the amplitude of the waveform in the outputsignal from the piezoelectric sensor 2 (sensor output waveform) isgradually enlarged in accordance with an increase of the frequency ofthe drive signal for the piezoelectric load 3. A predetermined threshold(voltage comparison level) shown in FIG. 2(C) is a voltage value set bythe reference voltage setting section 90 by inputting the voltage valueto the one input terminal of the voltage comparator 40. As shown in FIG.2(D), when the waveform of the output signal from the piezoelectricsensor 2 becomes larger than the predetermined threshold, the voltagecomparator 40 outputs a high-level signal.

The phase comparator 60 compares the phase of the output signal from thevoltage comparator 40 shown in FIG. 2(D) with the phase (phasereference) of the output signal from the phase reference forming section50 shown in FIG. 2(E). In this case, the timing charts show a case wherethe phase of the output signal from the voltage comparator 40 is notdelayed by the first phase correction section 51. As shown in FIG. 2(F),the phase comparator 60 outputs a high-level signal in the case wherethe rising point of the output signal from the phase reference formingsection 50 is earlier than the rising point of the output signal fromthe voltage comparator 40. On the other hand, the phase comparator 60outputs a low-level signal in the case where the rising point of theoutput signal from the phase reference forming section 50 is later thanthe rising point of the output signal from the voltage comparator 40.

A detailed description will be given for the operation for the phasecomparator 60 shown in FIG. 2(F) using FIGS. 2(D) and 2(E). In the casewhere the waveform of the output signal from the piezoelectric sensor 2is not matched with the voltage comparison level of the voltagecomparator 40, i.e., in the case where the amplitude of the outputsignal from the piezoelectric sensor 2 is smaller than the referencevoltage (voltage comparison level) set by the reference voltage settingsection 90, the phase comparator 60 outputs the high-level signal inregardless of the waveform of the output signal from the phase referenceforming section 50. First, when the output signal from the voltagecomparator 40 becomes the high level, the output signal from the phasecomparator 60 becomes zero (i.e., Hi-Z) in response to the change. Then,when the output signal from the phase reference forming section 50 risesup, the output signal from the phase comparator 60 becomes a high level.When the output signal from the voltage comparator 40 rises up afterthat time, the output signal from the phase comparator 60 becomes a zerolevel. As seen from FIG. 2(F), this state (generation of a pulse) occurstwice in this embodiment. Next, when the output signal from the voltagecomparator 40 rises up earlier than the rising of the output signal fromthe phase reference forming section 50, the output signal from the phasecomparator 60 becomes a low level. Then, when the output signal from thephase reference forming section 50 rises up, the output signal from thephase comparator 60 becomes the zero level again. After that, sameoperation is repeated. In this regard, since the case where the dutyratio is more than 50% is shown in the timing charts, the phasecomparator 60 compares the phases using the rising point of the outputsignal from the phase reference forming section 50 (see FIG. 5).

As shown in FIG. 2(G), the waveform of the output signal from the LPF 70responds to the waveform of the output signal from the phase comparator60. The output signal from the LPF 70 is raised up while the outputsignal from the phase comparator 60 is in the high level, kept at aconstant level while the output signal from the phase comparator 60 isin the zero level, and dropped down while the output signal from thephase comparator 60 is in the low level. Thus, in the case where therising point (rising timing) of the output signal from the voltagecomparator 40 is later than the rising point (rising timing) of theoutput signal from the phase reference forming section 50, the voltagevalue of the output signal from the LPF 70 rises up in order to heightenthe frequency of the output signal from the VCO 10. On the other hand,in the case where the rising point (rising timing) of the output signalfrom the voltage comparator 40 is earlier than the rising point (risingtiming) of the output signal from the phase reference forming section50, the voltage value of the output signal from the LPF 70 drops down inorder to lower the frequency of the output signal from the VCO 10.

In this way, in the resonance control apparatus 100 of the presentinvention, since the frequency of the drive signal of the piezoelectricload 3 is self-corrected based on the detected signal inputted from thepiezoelectric sensor 2 which detects the driving state of thepiezoelectric load 3 that is driving in response to the drive signal, itis possible to shorten (reduce) the time required to obtain the resonantfrequency of the piezoelectric load 3 in comparison with theconventional resonance control apparatus using a CPU to obtain theresonant frequency. Therefore, according to the resonance controlapparatus 100, it is possible to appropriately deal with posture controland the like in which a drive frequency of a piezoelectric load may bechanged rapidly.

Next, a description will be given for a resonant frequencycharacteristic in case of using a piezoelectric load with apiezoelectric effect. FIG. 3 is a graph illustrating a resonantfrequency characteristic of a piezoelectric load. It is well known thatthe piezoelectric load 3 has a resonant frequency characteristic shownin FIG. 3. The peak point (shown with diagonal lines) indicates aresonant frequency region (the piezoelectric load 3 has a resonant pointcorresponding to the resonant frequency fc). The resonant point dependson physical conditions such as a shape of a rotor, a wearing state ofthe rotor, humidity, load characteristic, or the like in the drivingdevice with the piezoelectric element whose resonant frequencyconstantly undergoes a change. In this way, the maximum energy can beobtained from the piezoelectric load 3 at the resonant frequency(resonant point), but it takes a long time until the conventionalresonance control apparatus obtains the resonant point by graduallyheightening the drive frequency. Therefore, the resonance controlapparatus 100 is constructed so as to take no account of (i.e., skip)the frequency range lower than the resonant frequency region shown inFIG. 3 by comparing the voltage value of the output signal from thepiezoelectric sensor 2 with the predetermined voltage value by means ofthe voltage comparator 40, to restore the frequency to the resonantpoint by comparing the phases in the range in which the output signalfrom the piezoelectric sensor 2 exceeds the threshold set in the voltagecomparator 40, and to obtain the resonant frequency (resonant point).Thus, according to the resonance control apparatus 100 of the presentinvention, it is possible to shorten (reduce) the time required toobtain the resonant frequency (resonant point) drastically.

Next, a description will be given for a piezoelectric response speedcharacteristic of a piezoelectric load. FIG. 4 is a graph schematicallyillustrating the relationship between a duty ratio and drive vectorratio of the drive signal. As shown in FIG. 4, the drive vector ratio ofthe piezoelectric load 3 becomes a maximum value (i.e., 100%) when theduty ratio is 50%, and becomes 0% when the duty ratio is 10% or 90%. Inthe range in which the duty ratio is from 10% to 50% or from 50% to 90%,the drive vector ratio moves (changes) substantially linearly. Thus, bycarrying out the PWM control for the piezoelectric load 3 in such arange, it is possible to control the drive vector of the piezoelectricload 3 like an analogue manner, i.e., with a continuous quantity.Further, as seen in FIG. 4, the graph of the piezoelectric responsespeed characteristic is line symmetry against the line on which the dutyratio is 50% (for example, a voltage value when the duty ratio is 80% issubstantially equal to a voltage value when the duty ratio is 20%).

Therefore, it is possible to expect that the piezoelectric load 3 bePWM-controlled using this characteristic. Namely, by using the dutyratio of the drive signal in the range of 10%-50% or 50%-90%, the driveoutput for the piezoelectric load 3 can be properly changed between 0%and 100%. This means that there is no need to control on/off of anactuator or the like (in this case, the piezoelectric load 3) accordingto the duty ratio of the drive signal as the PWM control for aconventional motor or the like. In the case where the piezoelectricelement is used as a load, the process to obtain the resonant frequency(resonant point) of the load must be carried out again when the actuatoror the like is turned on after it was turned off. However, since theresonance control apparatus 100 carries out the PWM control for the loadusing its piezoelectric response speed characteristic, it is possible tocontrol the drive vector ratio while the frequency of the drive signalis maintained at the resonant frequency of the piezoelectric load 3. Inthis regard, the “drive vector ratio” means the rate of the drive vectorcorresponding to each duty ratio in the case where it is determined thatthe drive vector (output) when the duty ratio of the drive signal is 50%is 100%.

Next, a description will be given for a phase comparison pointcharacteristic in the duty control. FIG. 5 is a diagram illustrating therelationship between the duty ratio controlled by the duty controlsection 30 and the phase comparing position determined by the phasereference forming section 50. FIG. 5(A) shows the output signals fromthe divider 20, the phase reference forming section 50, the first phasecorrection section 51 and the phase comparator 60 in the case where theduty ratio of the drive signal is less than 50%, and FIG. 5(B) shows theoutput signals from those components in the case where the duty ratio ofthe drive signal is more than 50%.

As the phase comparison point shown in FIG. 5, the phase referenceforming section 50 determines the trailing point of the output signalfrom the phase reference forming section 50 as a phase comparison pointin the phase comparator 60 in the case where the duty ratio of theoutput signal is less than 50%. On the other hand, the phase referenceforming section 50 determines the rising point of the output signal fromthe phase reference forming section 50 as a phase comparison point inthe phase comparator 60 in the case where the duty ratio of the outputsignal is more than 50%. In this way, the phase reference formingsection 50 changes the setting of the phase comparison point based onthe duty ratio because the point where the duty ratio is 0% (dutyratio<50%) or 50% (duty ratio>50%) is phase-locked in the waveform ofthe voltage comparison signal, i.e., the waveform of the output signalfrom the first phase correction section 51 shown in FIGS. 5(A) and 5(B)(i.e., the third waveform from the top in FIG. 5), which is outputtedfrom the voltage comparator 40 by comparing the detected signaloutputted from the piezoelectric sensor 2 with the predetermined voltagevalue. In the case where the rising point of the waveform of the outputsignal from the phase reference forming section 50 is determined as thephase comparison point when the PWM control is carried out at the pointin which the duty ratio is less than 50%, the control is not stabilizedbecause the phase comparator 60 compares the phases using the point atwhich the waveform of the output signal varies according to the controlof the duty control section 30 as a reference. The same is true in thecase where the duty ratio is more than 50%. Therefore, the resonancecontrol apparatus 100 is constructed so that the phase reference formingsection 50 can set the phase comparison point in addition to delay thephase of the output signal from the divider 20 for a predetermined time.

Next, a description will be given for the driver 80 to drive thepiezoelectric load (piezoelectric element) 3. FIG. 6 is a diagramschematically illustrating an example of a circuitry of the driver 80shown in FIG. 1. As shown in FIG. 6, the driver 80 includes fourtransistors Tr1, Tr2, Tr3 and Tr4, a voltage source, and a logicalnegation circuit NOT1.

When a square-wave whose duty ratio is controlled by the duty controlsection 30 is inputted to the driver 80 as a drive signal, during a highlevel of the drive signal, the transistors Tr2 and Tr3 are respectivelyturned on according to the high-level signal and the low-level signalthat is inverted in the logical negation circuit NOT1, whereby thecurrent Ib shown in FIG. 6 flows into the piezoelectric load 3 in thedirection shown as an arrow Ib. On the other hand, during a low level ofthe drive signal, the two transistors Tr1 and Tr4 are turned on, wherebythe current Ia shown in FIG. 6 flows into the piezoelectric load 3 inthe direction shown as an arrow Ia. The resonance control apparatus 100can supply the drive current similar to alternating current to thepiezoelectric load 3 using the driver 80 constructed in this manner.

Here, FIG. 7 is a diagram schematically illustrating waveforms ofsignals in the case where a drive analog control signal to be suppliedto drive the piezoelectric load 3 is one whose output is raised to apredetermined output level (voltage value) at a given rate (givenslope). When the signal having a predetermined frequency is outputtedfrom the divider 20 as a reference signal (see FIG. 7(B)), the dutycontrol section 30 sets the duty ratio of the drive signal inputted tothe piezoelectric load 3 so as to response to the variation in the driveanalog control signal shown in FIG. 7(A). Then, when the drive signalshown in FIG. 7(C) is inputted to the driver 80, an input signal havingthe waveform shown in FIG. 7(D) is supplied to the piezoelectric load 3.

In this regard, the case where the duty control section 30 sets the dutyratio in the range from 10% to 50% in the piezoelectric response speedcharacteristic of the piezoelectric load 3 shown in FIG. 4 is shown inFIG. 7. In this case, since the predetermined output level is set as thelevel at which the drive vector ratio of the piezoelectric load 3 is100%, as shown in FIG. 7, the duty ratios of the drive signal and theinput signal supplied to the piezoelectric load 3 becomes 50% when theoutput level (voltage value) of the drive analog control signal isrestored to the predetermined value.

Next, a description will be given for another embodiment of theresonance control apparatus 100 of the present invention. In the presentembodiment, the application of the resonance control apparatus 100 tonormal and reverse drive control for the piezoelectric load 3 or doublenormal drive control for the piezoelectric load 3 is shown. FIGS. 8(A)and 8(B) are diagrams illustrating examples of the structures in whichtwo vibrating elements 81, 81, or 81, 82 each including a piezoelectricload 3 that is controlled by the resonance control apparatus 100according to the present invention rotate a rotor 300. FIG. 8(A) showsthe case where the rotor 300 is rotated by means of a normal drivevibrating element 81 and a reverse drive vibrating element 82, and FIG.8(B) shows the case where the rotor 300 is rotated by means of twonormal drive vibrating elements 81, 81.

In this way, in the structure shown in FIG. 8(A), since the normal driveand reverse drive vibrating elements 81, 82 are applied to the one rotor300, the rotor 300 can be controlled so as to rotate in both rotativedirections. Further, in the structure shown in FIG. 8(B), since the twonormal drive vibrating elements 81, 81 are applied to the one rotor 300,the setting of the drive force for rotating the rotor 300 can be changedin the range from 0% to 200% theoretically.

In this regard, the number of the vibrating elements 81 and/or 82applied to the one rotor 300 is not limited to two shown in FIG. 8, butthe present invention may apply one or a plurality of vibrating elements81 and/or 82 to the one rotor 300. Further, in the structure shown inFIG. 8(A), it is preferred that the normal drive vibrating element 81and the reverse drive vibrating element 82 are respectively controlledby two duty control sections 30, 30 (see FIG. 9), and in the structureshown in FIG. 8(B), the two normal drive vibrating elements 81, 81 maybe respectively controlled by the two duty control sections 30, 30, ormay be controlled in cooperation with one duty control section 30.

A structure of a driver using the normal drive and reverse drivevibrating elements 81, 82 shown in FIG. 8(A), i.e., a piezoelectric load3 for normal drive and a piezoelectric load 3 for reverse drive isillustrated in FIG. 9, and waveforms of drive signals for driving thedrivers 80 a, 80 b are illustrated in FIG. 10. FIG. 9 is a diagramillustrating the partial structure of the resonance control apparatus100 according to the present invention in the case of respectivelycontrolling the normal drive and reverse drive of the piezoelectricloads 3 a, 3 b in the two vibrating elements 81, 82 shown in FIG. 8(A).

As shown in FIG. 9, a resonance control apparatus 100 for controllingthe drives of a normal-driving piezoelectric load 3 a and areverse-driving piezoelectric load 3 b includes a normal-driving dutycontrol section 31 and a reverse-driving duty control section 32 inplace of the duty control section 30 shown in FIG. 1. Further, theresonance control apparatus 100 includes a normal-driving driver 80 aand a reverse-driving driver 80 b in place of the driver 80. The CPU 1controls each of the normal-driving duty control section 31 and thereverse-driving duty control section 32. Thus, based on the referencesignal outputted from the divider 20, the normal-driving duty controlsection 31 sets the duty ratio of a signal for normal drive to drive thenormal-driving piezoelectric load 3 a, while the reverse-driving dutycontrol section 32 sets the duty ratio of a signal for reverse drive todrive the reverse-driving piezoelectric load 3 b.

In this regard, a normal-driving piezoelectric sensor (not shown in thedrawings), which moves in synchronization with the normal-drivingpiezoelectric load 3 a, is arranged close against the normal-drivingpiezoelectric load 3 a, while a reverse-driving piezoelectric sensor(not shown in the drawings), which moves in synchronization with thereverse-driving piezoelectric load 3 b, is arranged close against thereverse-driving piezoelectric load 3 b. By carrying out the processingof the detected signals (output signals) of these piezoelectric sensorsas mentioned above, it is possible to control the drives of thenormal-driving piezoelectric load 3 a and the reverse-drivingpiezoelectric load 3 b independently.

FIG. 10 is a diagram illustrating waveforms of the signals for normaldrive and reverse drive respectively controlled by normal-driving andreverse-driving duty control sections 31, 32 in response to a referencesignal. Based on the reference signal (see FIG. 10(A)) outputted fromthe divider 20 in the resonance control apparatus 100, the signal fornormal drive (see FIG. 10(B)) and the signal for reverse drive (see FIG.10(D)) respectively controlled by normal-driving and reverse-drivingduty control sections 31, 32 are inputted to the normal-driving driver80 a and the reverse-driving driver 80 b. Thus, the drive signal shownin FIG. 10(C) is inputted to the normal-driving piezoelectric load 3 a,while the drive signal shown in FIG. 10(E) is inputted to thereverse-driving piezoelectric load 3 b.

In this way, the resonance control apparatus 100 of the presentembodiment can control the normal drive and reverse drive of the twopiezoelectric loads 3 a, 3 b shown in FIGS. 8(A) and 9. When the twovibrating elements 81, 82 are controlled in response to the drivesignals shown in FIG. 10, first, the normal drive vibrating element 81is driven with the output of 100%, whereby the rotor 300 is rotated inthe direction X shown in FIG. 8(A). Subsequently, the outputs of thenormal drive and reverse drive vibrating elements 81, 82 becomes 0%during the period L shown in FIG. 10(E), thereby stopping the rotor 300.Next, as shown in FIG. 10(E), the reverse drive vibrating element 82 isdriven with the output of 100%, whereby the rotor 300 is rotated in thedirection Y shown in FIG. 8(A). In this case, as in the case shown inFIG. 7, the duty ratio in the range of 10%-50% is utilized in the inputsignals to the piezoelectric load 3 a, 3 b shown in FIG. 10. However, asmentioned above, the resonance control apparatus 100 can achieve thesame drive (operation) in the case where the drive signal is generatedusing the duty ratio in the range of 50%-90%.

As described above, in the resonance control apparatus 100 of thepreferred embodiments according to the present invention, the referencesignal outputted from the VCO 10 (i.e., reference signal generatingsection) is divided in the divider 20, the phase of the divided signalhaving the predetermined frequency is delayed by the phase referenceforming section 50, the detected signal outputted from the piezoelectricsensor 2 is compared with the predetermined voltage value by the voltagecomparator 40, the phase of the output signal from the voltagecomparator 40 (i.e., voltage comparison signal) is delayed by the firstphase correction section 51 as required, the phases of the phase-delayedsignals are compared by the phase comparator 60, and the output signalfrom the phase comparator 60 (i.e., phase comparison signal) is fed backto the VCO 10 after its high-frequency component is cut off by the LPF70.

In the resonance control apparatus 100 and the method of controlling theresonant device of the present invention, by voltage-comparing apredetermined voltage value with the waveform of the detected signalobtained by detecting the driving state of the piezoelectric load 3 tobe controlled using the piezoelectric sensor 2, the frequency of thedrive signal is rapidly heightened to the resonant frequency region ofthe piezoelectric load 3. Then, the resulting signal is fed back to theVCO 10 to obtain the resonant point (resonant frequency) of thepiezoelectric load 3, thereby controlling the driving of thepiezoelectric load 3 at the resonant point.

Therefore, according to the resonance control apparatus 100 and themethod of controlling the resonant device of the present invention, itis possible to shorten (reduce) the time required to obtain the resonantfrequency in the case where a rapid drive such as posture control isimplemented, and thus, it is possible to control the rest or movement ofan object in the posture control quickly. Therefore, this makes itpossible to control the driving of the piezoelectric load 3.

Further, since the resonance control apparatus 100 of the presentinvention generates a square-wave (voltage comparison signal) bycomparing the detected signal (analog signal) from the piezoelectricsensor 2 with a predetermined voltage value, the control after obtainingthe voltage comparison signal can be digitized. Thus, since thedigitized control sections (components) are increased in the entireapparatus, it is possible to integrate such control sections into an ICchip. Moreover, since it is possible to control the driving of thepiezoelectric load 3 without carrying out the processing such asintegral operation, frequency determining operation, and the like bymeans of the CPU 1, it is possible to downsize the circuitry of theresonance control apparatus 100.

Note that, in the embodiments, the drive control of the piezoelectricload 3 when the duty ratio of the drive signal is in the range of10%-50% has been described, but the present invention is not limited tothis range. As described above, in the present invention, the drivesignal whose duty ratio is in the range of 50%-90% may be utilized.

As described above, it should be noted that, even though the resonancecontrol apparatus and the method of controlling a resonant deviceaccording to the present invention have been described with reference tothe preferred embodiments shown in the accompanying drawings, thepresent invention is not limited to these embodiments, it is of coursepossible to make various changes and modifications to each element ofresonance control apparatus, and various elements described above can bereplaced with any other element capable of performing the same or asimilar function.

1. A resonance control apparatus for driving a resonant device having aresonance characteristic, the resonant device functioning as a resonantsensor, the apparatus comprising: a reference signal generating sectionfor generating a reference signal having a predetermined frequency inresponse to a voltage signal that is inputted into the reference signalgenerating section; a divider which divides the predetermined frequencyof the reference signal generated by the reference signal generatingsection to output a signal having a given frequency; a phase referenceforming section which delays a phase of the signal outputted from thedivider for a predetermined interval; a voltage comparator for comparinga voltage of the output signal from the resonant sensor with apredetermined voltage, the resonant sensor detecting the driving stateof the resonant device in synchronization with the driving of theresonant device; a phase comparator for comparing the phase of thesignal outputted from the voltage comparator with the phase of thesignal outputted from the phase reference forming section; and a dutycontrol section for controlling a duty ratio of the drive signalprovided for the resonant device based on the reference signal outputtedfrom the reference signal generating section.
 2. The apparatus asclaimed in claim 1, further comprising a low-pass filter which cuts outa high frequency component of the output signal from the phasecomparator wherein the output signal from the low-pass filterconstitutes the voltage signal inputted into the reference signalgenerating section.
 3. The apparatus as claimed in claim 1, wherein thephase reference forming section is constructed so as to be capable ofselecting either a rising edge or trailing edge of the signal delayed inthe phase reference forming section when the phase comparator comparesthe phases, based on the duty ratio of the drive signal controlled bythe duty control section.
 4. The apparatus as claimed in claim 1,wherein the duty control section drives the resonant device with theduty ratio in the range of either 10%-50% or 50%-90%.
 5. The apparatusas claimed in claim 1, wherein the output signal from the resonantdevice corresponds to a resonant frequency of the resonant device, andthe frequency of the drive signal outputted from the duty controlsection is controlled so as to be equal to the resonant frequency. 6.The apparatus as claimed in claim 5, wherein the apparatus carries outthe PWM control for the resonant device based on the duty ratio of thedrive signal controlled by the duty control section.
 7. The apparatus asclaimed in claim 6, wherein the PWM control is carried out so as tomaintain the resonant frequency of the resonant device.
 8. The apparatusas claimed in claim 1, further comprising a first phase correctionsection arranged between the voltage comparator and the phasecomparator, the first phase correction section correcting the phase ofthe signal outputted from the voltage comparator to output thephase-corrected signal to the phase comparator.
 9. The apparatus asclaimed in claim 8, further comprising a second phase correction sectionfor correcting the phase of the output signal from the duty controlsection in response to the phase of the resonant frequency of theresonant device.
 10. The apparatus as claimed in claim 1, furthercomprising a second duty control section having a function same as theduty control section, the second duty control section being arranged inparallel with the duty control section; wherein the two duty controlsections are respectively provided for normal drive and reverse drive ofthe resonant devices, and can control the duty ratios of the drivesignals for normal drive and reverse drive either independently orjointly.
 11. The apparatus as claimed in claim 1, further comprising atleast one duty control section having a function same as the dutycontrol section arranged in parallel with the duty control section;wherein at least two duty control sections among the duty controlsection and the at least one duty control section are provided fornormal drive of the resonant devices, and can control the duty ratio ofthe drive signals for normal drive either independently or jointly. 12.A resonance control apparatus for driving a resonant device having aresonance characteristic, the resonant device functioning as a resonantsensor, wherein the apparatus compares the phase of a drive signal forthe resonant device with the phase of an output signal from the resonantsensor, which is utilized as a feedback value for the resonant device,and outputs the drive signal to the resonant device in response to thedifference between the phases.
 13. A method of controlling a resonantdevice having a resonance characteristic, the resonant devicefunctioning as a resonant sensor, the method comprising the steps of:generating a reference signal having a predetermined frequency inresponse to a voltage signal to be inputted, the reference signal beinga drive signal for the resonant device; dividing the predeterminedfrequency of the reference signal to output a signal having a givenfrequency; delaying a phase of the output signal for a predeterminedinterval; comparing a voltage of the output signal from a resonantsensor with a predetermined voltage to output a voltage comparisonsignal, the resonant sensor detecting the driving state of the resonantdevice in synchronization with the driving of the resonant device; andcomparing the phase of the voltage comparison signal with the phase ofthe delayed signal to output a phase comparison signal, the phasecomparison signal corresponding to the voltage signal to be inputted.14. The method as claimed in claim 13, further comprising the steps of:controlling a duty ratio of the drive signal supplied to the resonantdevice; and carrying out the PWM control for the resonant device usingthe duty ratio of the drive signal.
 15. The method as claimed in claim14, wherein the duty ratio controlling step includes respectivelycontrolling duty ratios of two types of drive signals supplied to tworesonant devices, which are provided for normal drive and reverse driveof the two resonant devices, based on the reference signal, and the PWMcontrol carrying out step includes carrying out the PWM control for thetwo resonant devices using the duty ratios of the drive signals.
 16. Themethod as claimed in claim 14, wherein the duty ratio controlling stepincludes respectively controlling duty ratios of at least two drivesignals for normal drive supplied to at least two resonant devices basedon the reference signal either independently or jointly, and the PWMcontrol carrying out step includes carrying out the PWM control for theat least two resonant devices using the duty ratios of the at least twodrive signals.